The present application relates to a laser driving circuit employed in an optical-disk apparatus as a circuit provided with a recording compensation circuit and relates to the optical-disk apparatus for recording data onto an optical disk.
Each of FIGS. 1A to 1D is an explanatory diagram referred to in description of a general method for recording data WDT onto an optical disk. In this patent specification, the data WDT to be recorded onto an optical disk is referred to as recorded data WDT. To be more specific, FIG. 1A is an explanatory diagram showing the waveform of a recording clock signal WCK whereas FIG. 1B is an explanatory diagram showing the waveform of the recorded data WDT. FIG. 1C is an explanatory diagram showing recording marks WMK recorded on an optical disk whereas FIG. 1D is an explanatory diagram showing the waveform of light generated by a laser driven by the laser driving circuit cited above.
Data WDT is recorded onto most of optical disks by adoption of the so-called optical strength modulation method whereby marks WMK and spaces are formed on the optical disk in accordance with changes of the strength of the optical power (or light power) used in the process of recording the data.
In recording data WDT onto an optical disk in a recording process that generates only few errors, the changes of the optical power do not reflect changes of the recorded data WDT itself. Instead, the optical power has a waveform consisting of portions which each resemble a comb as shown in the explanatory diagram of FIG. 1D.
It is necessary to adjust the timing of each edge of the light emission pattern shown in the explanatory diagram of FIG. 1D by making an adjustment unit smaller than a channel clock interval Tw shown in the explanatory diagram of FIG. 1A. Typical examples of the adjustment unit are Tw/40, Tw/32 and Tw/16.
The devisal to create the light emission pattern like the one shown in the explanatory diagram of FIG. 1D is referred to as recording compensation whereas the timing of each edge of the light emission pattern is determined by a recording compensation circuit mentioned before in accordance with recorded data WDT like one shown in the explanatory diagram of FIG. 1B.
Each of FIGS. 2A and 2B is an explanatory diagram showing a typical configuration of a laser driving system, which includes the aforementioned laser driving circuit and the recording compensation circuit cited earlier, in an optical-disk apparatus.
The existing laser driving system 1 shown in the explanatory diagram of FIG. 2A as a system of an optical-disk apparatus employs an optical head 2 and a drive substrate 3. The optical head 2 is a component on which a semiconductor laser and optical components are mounted. On the other hand, the drive substrate 3 is a substrate on which control circuits are mounted.
In order to make the optical head 2 movable in the radial direction of the optical disk, the optical head 2 and the drive substrate 3 are connected to each other by making use of a flexible substrate 4.
In the existing laser driving system 1, a recording compensation circuit 5 is mounted on the drive substrate 3 as shown in the explanatory diagram of FIG. 2A. The recording compensation circuit 5 mounted on the drive substrate 3 supplies a signal indicating a light emission timing to an IC mounted on the optical head 2 to serve as a laser driving circuit 6 by way of the flexible substrate 4. On the other hand, a laser-power control circuit mounted on the drive substrate 3 applies a voltage indicating a laser power (the light or optical power mentioned before) to the laser driving circuit 6 through the flexible substrate 4. In accordance with the voltage indicating a laser power, the laser driving circuit 6 generates a driving current for driving a semiconductor laser LD to enter a state of emitting light.
The signal indicating a light-emission timing has timing information expressed in terms of units which are each smaller than the channel clock interval Tw shown in the explanatory diagram of FIG. 1A. With recording-speed improvements made in recent years, however, it became difficult to transmit the signal indicating a light emission timing to the laser driving circuit 6 by way of the flexible substrate 4.
In order to solve the problem described above, in the typical configuration of a solution laser driving system 1A shown in the diagram of FIG. 2B to serve as a solution to the problem, it is the laser driving circuit 6A that includes the embedded recording compensation circuit 5. Instead of supplying information on a light emission timing to the recording compensation circuit 5 by way of the flexible substrate 4, the drive substrate 3A outputs a recording clock signal WCK and the recorded data WDT to the recording compensation circuit 5 by way of the flexible substrate 4. Since each of the recording clock signal WCK and the recorded data WDT is a signal having granularities each equal to the channel clock interval Tw, the recording clock signal WCK and the recorded data WDT are both hardly affected by the transmission characteristic of the flexible substrate 4.